The present invention relates to shaped charges for generating a metallic jet. More particularly, the present invention relates to an improved shaped charge that incorporates a lens shaped waveshaper to modify an explosive wave impacting the liner in a shaped charge.
Shaped charges are used in the oil and gas industry and in other fields to pierce metal, concrete, and other solid materials. In an oil or gas well, a metallic casing is cemented to the borehole walls to maintain the borehole integrity. Shaped charges are incorporated in a hollow carrier gun or a strip positioned in the casing. The shaped charges are activated to pierce the well casing and the geologic formation at the hydrocarbon producing zone. The hydrocarbons enter the casing through such perforations and are transmitted to the well surface.
Conventional shaped charges are constructed with a charge case, a hollow conical liner within the case, and a high explosive material positioned between the liner and case. A detonator is activated to initiate the explosive material to generate a detonation wave. This wave collapses the liner and a high velocity metallic jet is formed. The jet pierces the well casing and geologic formation, and a slow moving slug is simultaneously formed. The jet properties depend on the charge shape, the energy released, and the liner mass and composition.
The penetrating power of the jet is determined by the jet velocity and other factors. One factor affecting jet velocity is the transfer of kinetic energy between the detonation wave and the liner. This transfer depends on the energy imparted by the detonation wave, the propogation of the detonation wave as a function of time, and the liner shape.
Waveshapers have been incorporated in shaped charges to delay a portion of the detonation wave, and to redirect the propogation of the detonation wave. Conventional waveshapers typically convert the point initiated detonation front to a peripherally initiated detonation within the shaped charge. Such waveshapers are typically constructed with wood, Teflon, plastic or other nonmetallic materials and redirect the detonation waves by partially inhibiting the transport of the detonation waves through the nonmetallic material.
Although conventional waveshapers are useful in shaping the detonation wave from a purely divergent wavefront, such waveshapers do not efficiently focus the energy of the detonation wave into contact with the shaped charge liner. Accordingly, a need exists for an improved shaped charge that efficiently focus the detonation waves.